Here’s Why Exercise — Without Dieting — Doesn’t Work for Weight Loss

The benefits of regular exercise are many: a healthier heart, improved metabolism and weight management, along with stronger bones and muscles. Not to mention exercise is part of a formula that can help prevent a long list of chronic diseases, including many cancers.

But is exercising — without adhering to a healthy diet — an effective strategy for weight loss? The short answer: No. As good as exercise is for you, it won’t help much without dietary modifications if you’re trying to lose weight and fend off heart disease, diabetes and other ailments, dietitians and researchers say.

The most recent study to examine exercise-only weight-loss plans followed women who engaged in exercise classes three times per week for four or eight weeks — but who did not change their diets. The result: They failed to lose weight.

As you get older, healthier eating — focusing on fruits, vegetables, whole grains and lean proteins — becomes even more crucial as exercising is more challenging, says Natacha Borrajo, a registered dietitian with Baptist Health Primary Care.

“When we’re younger, our metabolism is high and we can sometimes eat whatever we want — but that starts catching up with us over time,” says Ms. Borrajo.

In the recent study, researchers at Bangor University in the United Kingdom broke down their study into two parts, both involving young women. For the first experiment, 34 women aged 18 to 32 years performed circuit exercise sessions, three times per week for a total of four weeks. The second experiment involved 36 women of the same age group who took part in the same training sessions, but for a total of eight weeks.

The goal of the study was to determine whether or not exercise alone would lead to weight loss in the women, but the participants were not told this. Instead, they were told that the study would examine the effects of exercise on cognition and cardio-respiratory fitness. At the end of the four- and eight-week programs, the researchers found that none of the women lost weight. The subjects included a mix of women who were lean, overweight, or obese prior to the study.

The researchers found that women who were overweight or obese experienced increased hunger. Meanwhile, the women who were lean at the beginning of the study saw an increase in muscle mass after the exercise training sessions.

The takeaway is that regular exercise is vital for good health, but has no benefits for weight loss if not accompanied by healthier eating, according to study co-author Dr. Hans-Peter Kubis, of the School of Sport, Health & Exercise Sciences at Bangor University.

It all relates back to our metabolism, says Ms. Borrajo.

“Exercise alone is not going to help you in the long run,” she says. “It might be a good habit to create, but then you need to start incorporating good eating habits if you’re ever going to maintain a healthy weight.”

Other studies have found that shifting to healthier eating, with increased fiber and less “added sugars,” can achieve weight loss with minimal exercise. But physical activity is an integral element of the formula for healthy living, as well as maintaining the proper weight.

General U.S. guidelines for achieving optimal health call for 150 minutes a week of moderate-intensity aerobic activity, 75 minutes of vigorous-intensity aerobic activity, or an equivalent mix of the two.